In a steel mill or the like the workpieces are passed along production lines where they are rolled, sawed, bored, coated, and subject to various treatments. The workpieces are usually elongated and displaced longitudinally, that is parallel to their longitudinal directions, in the individual lines. Movement from line to line must be transverse, since the lines are usually arranged parallel to one another.
To this end the downstream or output end of one production line is normally separated from the upstream or intake line of the next line by a table formed by a plurality of support beams extending between the two lines horizontally and parallel to each other but transverse to the lines. These beams have upper surfaces that define a plane and serve to support the workpieces between operations. One side of the table can be loaded directly from the line by a piece of automatic equipment, or by a fork lift. From the opposite side the workpieces can be taken off by another conveyor, fork lift, or the like.
To displace the workpieces transversely on the table, and to rearrange them thereon as such a table is frequently used as a depot, at least two synchronously operating carriages or wagons are used. Each rides on a vertically displaceable guide beam extending parallel to the support beams. When in an upper position the guide beam holds the carriage at least partially above the plane of the table, and when in a lower position the carriage is spaced below this plane. Thus the carriages can be raised up underneath a load to be moved transversely, raising it slightly above the table so it can be displaced transversely to its longitudinal direction and to the transport direction of the lines.
The carriages are connected to one stretch of a flexible drive element, e.g. a chain or cable, that is reeved normally as an endless loop over two wheels constituted as pulleys or sprockets. One of these wheels can be driven in either direction to move the carriages horizontally. Once the carriages have raised up underneath and picked up a load, the chain then is appropriately driven to position the picked-up load transversely.
Obviously as each carriage is raised and lowered it deflects the drive element up and down, respectively. This adds considerably to the tension in this element needed to position the carriage accurately. In addition the actuator system that raises the carriages and the load they carry must also provide the force necessary to thus deflect the drive element, force that serves no useful function. This extra tension subjects the drive element and associated structure to considerable wear. In addition downward displacement of the carriage must be effected positively, gravity alone cannot suffice to exert enough force to deflect the drive element down. This is another waste of energy.